Alpha Technologies Cordex Controller Ver.2.0 - Manual (Page 104)

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10 Simple Network Management Protocol (SNMP)
10.1 Overview
SNMP was developed in 1988 as an operating system for the management of the data flow from a series of
remote information generators, or Agents, connected to a central computer, or Manager, by way of a network.
The software installed in the Agent (whether it is supplied by Alpha or customer supplied) uses SNMP to translate
the data stream into a format that can be readily downloaded by way of the client's network to the Manager
computer located at the customer's Central Office used as a hub for the network.
Each Agent collects data from a source, translates that data into the SNMP format and then transmits the
translated data, when requested, to the Manager computer.
In the case of a network of Alpha Power Systems, the data stream from an individual power plant is developed
through the CXC System Controller, which directly interfaces with that power system. This data stream is referred
to as the Management Information Base or MIB, see 0.
An SNMP may have a number of simple messages that can be sent directed towards the retrieval of single or
multiple object variables or to establish the value of a single variable.
The Alpha SNMP Agent software employs an event notification called a "Trap" to the management system to
identify the occurrence of conditions that exceed a predetermined value such as an alarm event. Trap Protocol
Data Units or PDU’s have the following format:
Enterprise – identifies the type of object causing the trap.
Agent Address – IP address of agent that sent the trap.
Generic Trap ID – the common standard traps.
Specific Trap ID – proprietary or enterprise trap.
Time Stamp – when trap occurred in time ticks.
10.1.1 Outline of the SNMP Protocol
 Each SNMP managed object belongs to a community.
 Network Management Station (NMS) may belong to multiple communities.
 A community is defined by a community name, which is an Octet String with 0 to 255 octets in length.
 Each SNMP message consists of three components:
1. Version number
2. Community name
3. Data - a sequence of PDU's associated with the request.
10.1.2 Underlying Communication Protocols
SNMP assumes that the communication path is a connectionless communication sub-network. In other words, no
prearranged communication path is established prior to the transmission of data. As a result, SNMP makes no
guarantees about the reliable delivery of the data. Although in practice most messages get through, and those
that don't can be retransmitted. The primary protocols that SNMP implements are the User Datagram Protocol
(UDP) and the Internet Protocol (IP). SNMP also requires Data Link Layer protocols such as Ethernet or Token
Ring to implement the communication channel from the management to the managed agent.
SNMP's simplicity and connectionless communication also produce a degree of robustness. Neither the manager
nor the agent relies on the other for its operation. Thus, a manager may continue to function even if a remote
agent fails. When the agent resumes functioning, it can send a trap to the manager, notifying it of its change in
operational status. The connectionless nature of SNMP leaves the recovery and error detection up to the
Manager computer and even up to the Agent.